Dual-stage positioning system

ABSTRACT

A positioning system for positioning a patient support in an imaging device is disclosed herein. The positioning system includes a fine positioning subsystem coupled to the patient support and adapted to position the patient support with fine precision along the X-axis; and a coarse positioning subsystem coupled to the fine positioning subsystem and adapted to position the patient support with coarse precision along the X-axis. In an embodiment, the fine positioning subsystem and the coarse positioning subsystem are a dual-stage drive positioning system, with the first drive including a screw mechanism and the second drive including a prime mover. In an embodiment, a programmer is provided for configuring the fine positioning subsystem to align the patient support based on a velocity profile.

FIELD OF THE INVENTION

This invention generally relates to positioning systems. Moreparticularly, it relates to a positioning system with a dual-stage driveassembly.

BACKGROUND OF THE INVENTION

In imaging devices, the position of the object to be imaged and itscontrol are often critical. The proper positioning or aligning of theobject is required to obtain images of high quality. In diagnosticimaging devices, the positioning of the patient is achieved by aligningthe patient table or patient support surface with reference to theradiation source and the radiation detector.

Typically, positioning systems for a patient support in a diagnosticmedical imaging equipment include mechanisms for effecting longitudinaland lateral movement to the patient support for enabling convenientpositioning of a patient lying on or otherwise supported by the patientsupport for medical examination.

Known configurations of a positioning system for a patient supportinclude a longitudinal drive mechanism and a lateral drive mechanismhaving one of a manually operable configuration or a drive motor.

However, these known configurations do not provide an optimumpositioning and arrangement of the drive mechanisms. For example, incomputer tomography (CT) imaging systems, the patient support surfaceoften needs to be placed with micrometer precision. Some known CT tablesuse a screw drive or friction drive to convert the rotary motion of ascrew rod to linear motion of the patient support. A servomotor iscoupled to drive the screw rod in a closed loop to achieve bettercontrol and precision. However, such CT tables will not yield therequired precision for positioning patients, especially if accuracies inthe range of one micrometer are needed.

Thus it would be desirable to provide a positioning system capable ofpositioning an object with enhanced precision in comparison to knownpositioning systems. It would also be desirable to provide a positioningsystem for use in medical imaging applications where the patient needsto be accurately positioned.

SUMMARY OF THE INVENTION

The above-mentioned shortcomings, disadvantages and problems areaddressed herein which will be understood by reading and understandingthe following specification.

The present invention provides a positioning system for positioning apatient support in an imaging device. The positioning system comprises:a fine positioning subsystem coupled to the patient support, adapted forpositioning the patient support with fine precision; and a coarsepositioning subsystem coupled to the fine positioning subsystem, adaptedfor positioning the patient support with coarse precision, wherein thefine positioning subsystem and coarse positioning subsystem areconfigured to position the patient support along an X-axis. In anembodiment, the fine positioning subsystem is configured to position thepatient support with micrometer precision, and the coarse positioningsubsystem is configured to position the patient support with millimeterprecision. In an embodiment the fine positioning subsystem is configuredto position the patient support with a precision of one micrometer for aspecified range of 0-300 millimeters along the X-axis. In an embodimentthe coarse positioning subsystem is configured to position the patientsupport with a precision of one millimeter for a range of 0-2000millimeters along the X-axis.

In another embodiment, a positioning system with a dual-stage driveassembly for an imaging device is described. The positioning systemcomprises: a patient support capable of moving along an X-axis; a firstdrive coupled to the patient support, adapted for fine positioning ofthe patient support with fine precision along the X-axis; and a seconddrive coupled to the first drive, adapted for coarse positioning of thepatient support with coarse precision along the X-axis. In an embodimenta programmer is provided for configuring the fine positioning subsystemto move and position the patient support based on a velocity profile.The velocity profile may include mapping velocity of the patient supportwhile scanning along the X-axis over volume of a scanned object. Thevelocity of the patient support may be directly proportional to thecross section of the object being scanned.

In yet another embodiment a method of positioning a patient in animaging device is provided. The method comprises the steps of: (a)aligning a patient table along an X-axis using a coarse positioningsubsystem; (b) fine tuning the alignment of the patient table with fineprecision along the X-axis using a fine positioning subsystem; (c)activating the fine positioning subsystem to position the patient tableusing a velocity profile; and (d) adjusting the position of the patienttable using the velocity profile. In an embodiment, the velocity profileincludes mapping of velocity of the patient support, in an imagingdevice over volume or cross section of a scanned object.

Various other features, objects, and advantages of the invention will bemade apparent to those skilled in the art from the accompanying drawingsand detailed description thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an imaging device capable of using apositioning system described in an embodiment of the invention;

FIG. 2 is a schematic diagram of a positioning system as in anembodiment of the invention;

FIG. 3 is a schematic diagram of a fine positioning subsystem asdescribed in an embodiment of the invention;

FIG. 4 is a schematic diagram of a coarse positioning subsystem asdescribed in an embodiment of the invention; and

FIG. 5 is a flow chart indicating a method of positioning a patient inan imaging device as described in an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description, reference is made to theaccompanying drawings that form a part hereof, and in which is shown byway of illustration specific embodiments that may be practiced. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the embodiments, and it is to be understood thatother embodiments may be utilized and that logical, mechanical,electrical and other changes may be made without departing from thescope of the embodiments. The following detailed description is,therefore, not to be taken as limiting the scope of the invention.

In an embodiment, a dual-stage positioning system is disclosed. Thepositioning system is provided with a coarse positioning subsystem forproviding a reference and a fine positioning subsystem for providinghigh precision alignment.

In various embodiments a positioning system using a dual-stage driveassembly for an imaging device is disclosed. The embodiments, however,are not so limited, and may be implemented in connection with othersystems such as industrial imaging system, tracking systems, variouspositioning systems etc. In an embodiment, the positioning systemimparts very high precision for the required range and coarse precisionfor the remaining displacement range. In another embodiment, themovement of the object being scanned is programmed as per the crosssectional volume of the part. A velocity profile, a mapping between thevelocity of the patient support over a cross section of area or volumeof the object being scanned is calculated. The velocity of the patientsupport is directly proportional to the volume of the object. In anembodiment, the movement of the patient support is programmed based onthe velocity profile. Various parts require different types of velocityprofiles, which can be preprogrammed and easily executed wheneverrequired.

FIG. 1 is a schematic diagram of an imaging device capable of using apositioning system described in an embodiment of the invention. Theimaging device 100 can be one of a computed tomography device, apositron emission tomography device, a magnetic resonance imagingdevice, an ultrasound-imaging device and an X-ray device. One skilled inthe art will however appreciate that, the imaging device is not limitedto the examples mentioned above and the invention shall have full scopeof the claims.

In an embodiment, the imaging device 100 comprises an imaging gantry105. The imaging gantry 105 includes a tunnel 125 for receiving apatient 110 and a radiation source 130 for providing radiations. Apatient support 115 having a patient support surface is provided forengaging and supporting the patient 110. A positioning system 120 isprovided for moving and aligning the patient support 115, which isreceived in the tunnel 125 of the imaging device 100. For better qualityimages and desired results the patient support needs to be positionedwith fine precision. In an embodiment, the fine precision is in therange of micrometer precision. In an embodiment, the positioning systemis designed to align or position the patient support along an X-axiswith a precision of one micrometer for a range of 0-300 millimeters. Thepositioning system will be explained in detail with reference to FIG. 2.While the patient support 115 in FIG. 1 includes a patient supportsurface upon which a patient may lie down, the patient support may alsoinclude a patient support surface that supports a patient or a portionof the patient in another orientation, such as a patient who is standingor arranged vertically while pressed against a surface of the patientsupport, or whose body is strapped to, or otherwise attached or coupledto, the support surface. The imaging device is one of a computedtomography device, a positron emission tomography device, a magneticresonance imaging device, an ultrasound imaging device and an X-raydevice.

FIG. 2 illustrates a schematic diagram of a positioning system as in anembodiment of the invention. The positioning system comprises a patientsupport 215 having a patient support surface and a positioning system220. The patient support 215 may comprise a carrier and two or moreelongated rails (not shown). The carrier can be used for engaging andsupporting a patient. The elongated rails can be provided at the bottomside of the carrier and can extend between the opposing sides of thepatient support 215. The elongated rails are provided for co-operationduring longitudinal movement of the carrier. The patient support 215 isconfigured to move along the X-axis of an imaging device or laterallyusing the positioning system 220.

The positioning system 220 comprises a fine positioning subsystem 221and a coarse positioning subsystem 226. The patient support 215 is apatient table. The patient support 215 is coupled to the finepositioning subsystem 221 through a fine feed 222. The fine feed 222 maybe any mechanism, which can connect the fine positioning subsystem 221to the patient support 215. This may include a clamp, or a bracket orany other holding means. The fine positioning subsystem 221 is capableof aligning or positioning the patient support 215 with a precision of amicrometer. In an embodiment, the fine positioning subsystem 221 alignsthe patient support 215 with a precision of one micrometer for a rangeof 0-300 millimeters along the X-axis of the imaging device. However, itwill be understood that the fine positioning system 221 may position thepatient support 215 with other fine precisions. The fine positioningsubsystem 221 is further coupled with the coarse positioning subsystem226. In an embodiment the fine positioning subsystem 221 is a precisionscrew mechanism. The precision screw mechanism includes a screwarrangement 223 and an electric motor 225 coupled to the screwarrangement. The electric motor 225 is connected to the screwarrangement 223 by means of a timer belt 224. The fine positioningsubsystem will be explained in detail in FIG. 3.

The coarse positioning system 226 is configured to be prime mover. In anembodiment the coarse positioning subsystem 226 includes one or moredouble-end shaft motors (not shown) comprising shafts that extendoutwardly in opposite directions. One or more timer pulleys 227 can bemounted on each end of the double-end shaft motor. One or more belts 228can extend over the timer pulleys 227. The belts can be coupled to thedouble-end shaft motor through a coupling device (not shown). The belt228 can also be coupled to fine positioning subsystem 221 through acoarse feed 229. As the fine positioning subsystem 221 is coupled withthe patient supporting 215, the coarse positioning subsystem 226 will beable to move the patient support 215 laterally. The coarse positioningsubsystem 226 is configured to align the patient support with aprecision of one millimeter for a range of 0-2000 millimeters. Howeverthe various ranges of precisions may be achieved using the same conceptbut with different design as per the requirements of the particularapplication. By using the coarse positioning subsystem 226 a referenceposition is achieved, and using the fine positioning subsystem 221 thepatient support 215 is aligned or positioned with micrometer precision.The coarse positioning subsystem using double-end shaft motors will beexplained in detail in FIG. 4.

In an embodiment the coarse positioning subsystem is configured to be aprime mover operating in a closed loop. However the coarse positioningsystem may be configured to be a coarse screw drives mechanism, ahydraulic drive mechanism and friction drive mechanism.

FIG. 3 illustrates schematic diagram of a fine positioning subsystem asdescribed in an embodiment of the invention. In an embodiment, the finepositioning subsystem is configured to be a first drive 321. An imagingdevice is provided with a patient support 315 having a patient supportsurface for supporting and engaging a patient. The first drive isconnected to the patient support 315 through a fine feed 323. The finefeed 323 may be any mechanism, which can connect the fine positioningsubsystem 321 to the patient support 315. This may include a clamp, abracket or any other holding means. The first drive 321 includes a veryhigh precision screw drive mechanism operating in a closed loop. Theprecision screw drive mechanism includes a screw arrangement 322 and anelectric motor 325 connected with the screw arrangement 322 for drivingthe screw arrangement. The screw arrangement 322 is coupled with theelectric motor 325, for driving the screw arrangement, through a timerbelt coupled drive 324. In an embodiment the screw used in the screwarrangement is a ground ball screw with preloading for backlash freeexecution. In an embodiment the electric motor is a stepper or aservomotor.

In an embodiment the fine positioning subsystem 321 is programmed tomove the patient support 315, based on a velocity profile. The finepositioning subsystem 321 is provided with a programmer 326 forconfiguring the fine positioning subsystem 321 for moving or positioningthe patient support 315 based on a velocity profile. The programmer 326is coupled with the electric motor 325. The displacement of scanningpart of the object being scanned can be programmed as per the crosssectional area or volume of the part. The velocity of patient movingalong the X-axis through the scanning beam in an imaging device isdirectly proportional to the volume of the object being scanned. Thus ina particular area of cross section, if the volume is more, then scanningtime will be more compared to parts with lesser area of cross section orvolume. By programming the movement of the patient support surface thescanning time may be reduced. In effect, if a part with less volume ofcross section is being scanned, it requires less time and hence thepatient support may be moved quickly. This will reduce the time of scan.Various parts of the object will have different types of velocityprofiles, which can be preprogrammed and easily executed wheneverrequired.

For programming the displacement of the patient support the velocityprofile of the object is obtained. The velocity profile includes mappingof velocity of the patient support in an imaging device over the crosssectional area/volume of the object being scanned.

FIG. 4 illustrates a schematic diagram of a coarse positioning subsystemas described in an embodiment of the invention. In an embodiment thecoarse positioning subsystem is configured to be a second drive 400. Thecoarse positioning subsystem is provided to operate in a closed loop. Animaging device is provided with a patient support 415 having a patientsupport surface for supporting and engaging a patient. The patientsupport 415 can comprise a carrier 450 that engages and supports apatient. The patient support 415 is a patient table capable of movingalong the X-axis of the imaging device. The patient support 415 can alsocomprise structural members such as elongated rails 445 for enabling themovement of the carrier 450 along a horizontal or X-axis. The carrier450 is slidably mounted on the elongated rails 445 of the patientsupport 415. The second drive 400 for moving the patient support 415 isa rotary-to-linear motion converter. The second drive 400 can compriseone or more double-end shaft motors 425. The double-end shaft motor 425can be a stepper or a servomotor. Operation of the double-end shaftmotor 425 causes a linear motion of the patient support 415. The seconddrive 400 is connected with the first drive through a coarse feed 229.The coarse feed 229 includes any holding or attaching means capable ofattaching the second drive to the first drive. This may includesbrackets, clamps or any other holding means. One or more belts 440 forexample; tooth belt can be coupled to the double end shaft motor 425 viaa coupling device 410. The coupling device 410 provides smootherengagement and eliminates chatter. The coupling device 410 can beconfigured to be an electro-mechanical clutch.

The second drive 400 may further comprise multiple timer pulleys 427rotatably placed beneath the patient support 415. Operation of thedouble-end shaft motor 425 causes rotation of the timer pulley 405. Thetimer pulleys 405 drive the belt 440 extending between the timer pulleys405. The belt 440 in turn secures the first drive 212 through the coarsefeed. The first drive 212 is coupled to the patient support through thefine feed. Therefore, the rotation of the timer pulleys 405 causes alinear movement of patient support 415.

Each timer pulley 405 can be directly coupled to a feedback device 435at a first end. The feedback device 435 is a sensor assembly providingan indication of an absolute position of the patient support 415. Thesensor assembly comprises a magnet secured to the carrier 450 and amagnetic absolute linear position sensor secured to one of the elongatedrails 445 of the patient support 415. The relative position of thecarrier 450 with respect to the magnetic absolute linear position sensorof the elongated rails 445 can be determined from the output signalprovided by the magnetic absolute linear position sensor. The feedbackdevice 435 can be configured to be an encoder. More particularly, thefeedback device 435 can be configured to be an absolute encoder forgreater positioning accuracy.

In an embodiment the output of the feedback device 435 may be providedto the programmer 326. This will allow the programmer 326 to select thedesired velocity profile based on the position of the patient support.

The timer pulley 405 can also be coupled to a brake device 430 at asecond end. The brake device can be a positive clamping device. Thebrake device ensures that the carrier position is not disturbed afterthe carrier is positioned at a predetermined position. This provides areference position for the first drive. Further, the brake device 430can configured to be an electro-mechanical brake for better safety.

In an embodiment the second drive is configured to be a coarse screwmechanism. This includes a screw arrangement capable of positioning thepatient support coarsely. The coarse screw mechanism further includes anelectric motor coupled to the screw arrangement through a belt.

In an embodiment the second drive is configured to be a set of hydrauliccylinders used to move the patient support along the X-axis. Fewcylinders placed in a particular configuration would help to attain therequired coarse position.

The fine positioning subsystem is actuated once an initial referenceposition is reached and the electro mechanical brakes actuated. Thesepair of brakes will rigidly hold the patient support in its initialreference position and this will act as a reference position to the finepositioning subsystem. This fine positioning subsystem has a veryprecise screw mechanism coupled with a stepper motor or servo motor in aclose loop. The displacement least count can be of one micrometer as thestroke is limited to 300 mm only. The rigidity, accuracy, repeatabilityand control will be absolute. The errors will be reduced drasticallybecause of the range control and least count.

FIG. 5 illustrates a flow chart indicating a method of positioning apatient in an imaging device as described in an embodiment of theinvention. The method of positioning is illustrated in 500. At block510; a patient table is aligned along the X-axis using a coarsepositioning subsystem. At block 520, the alignment of the patient tableis fine tuned using a fine positioning subsystem. The patient table maybe aligned with a precision of up to 1 millimeter for a range of 0-300micrometers. At block 530, the fine positioning subsystem is actuated toposition the patient table using a velocity profile. In an embodimentthe velocity profile includes mapping of velocity the patient support inan imaging device over volume of a scanned object. At block 540,adjusting the position of the patient table using the velocity profile.

The manufacturing and production of the positioning system is simplifiedwhen compared to the conventional positioning system using super drivesystems like magnetic motors or linear motors to achieve similaraccuracies and least count. The manufacturing cost is saved around 40%.The positioning system requires less assembly time and can beaccommodated easily due to the flexibility of the tooth belt used.Therefore the manufacturing, assembling, transport and handling of thepositioning system are simple, cheap and reliable.

Since the positioning of the patient support is programmed based on thevelocity profile, the scanning time can be reduced. As dual stagepositioning system is used, the patient support and the patientsupported thereby may be placed with very high precision.

Thus various embodiments of positioning system are disclosed. However,it should be noted that the invention is not limited to this or anyparticular application or environment. Rather, the technique may beemployed in a range of applications, including medical imaging systems,industrial imaging systems, tracking system or any other positioningtechnology, to mention a few. The invention also discloses a method ofaligning a patient for exposing to radiations.

While the invention has been described with reference to preferredembodiments, those skilled in the art will appreciate that certainsubstitutions, alterations and omissions may be made to the embodimentswithout departing from the spirit of the invention. Accordingly, theforegoing description is meant to be exemplary only, and should notlimit the scope of the invention as set forth in the following claims.

1. A positioning system for positioning a patient support in an imagingdevice comprising: a fine positioning subsystem coupled to the patientsupport, adapted for positioning the patient support with fineprecision; and a coarse positioning subsystem coupled to the finepositioning subsystem, adapted for positioning the patient support withcoarse precision, wherein the fine positioning subsystem and the coarsepositioning subsystem are configured to position the patient supportalong an X-axis.
 2. The positioning system as in claim 1, wherein thefine positioning subsystem is configured to position the patient supportwith micrometer precision, and the coarse positioning subsystem isconfigured to position the patient support with millimeter precision. 3.The positioning system as in claim 1, wherein the fine positioningsubsystem is configured to position the patient support with a precisionof one micrometer for a range of 0-300 micrometers along the X-axis. 4.The positioning system as in claim 1, wherein the coarse positioningsubsystem is configured to position the patient support with a precisionof one millimeter for a range of 0-2000 millimeters along the X-axis. 5.The positioning system as in claim 1, wherein the fine positioningsubsystem comprises a screw drive mechanism operating in a closed loop.6. The positioning system as in claim 5, wherein the screw drivemechanism includes a screw arrangement and an electric motor coupled tothe screw arrangement and configured to drive the screw arrangement. 7.The positioning system as in claim 6, wherein the screw drive mechanismis coupled to the patient support through a fine feed.
 8. Thepositioning system as in claim 1, wherein the coarse positioningsubsystem is configured to be a prime mover operating in a closed loop.9. The positioning system as in claim 8, wherein the coarse positioningsubsystem includes a screw drive mechanism, hydraulic drive mechanism orbelt drive mechanism.
 10. The positioning system as in claim 1, whereinthe fine positioning subsystem is coupled to the coarse positioningsubsystem through a coarse feed.
 11. The positioning system as in claim1, wherein the imaging device is one of a computed tomography device, apositron emission tomography device, a magnetic resonance imagingdevice, an ultrasound imaging device and an X-ray device.
 12. Apositioning system with a dual-stage drive assembly for an imagingdevice, comprising: (a) a patient support capable of moving along anX-axis; (b) a first drive coupled to the patient support, adapted forfine positioning of the patient support with fine precision along theX-axis; and (c) a second drive coupled to the first drive, adapted forcoarse positioning of the patient support with coarse precision alongthe X-axis.
 13. The positioning system as in claim 12, wherein the firstdrive is configured to position the patient support with micrometerprecision, and the second drive is configured to position the patientsupport with millimeter precision.
 14. The positioning system as inclaim 12, wherein the patient support includes a carrier and at leasttwo pairs of elongated rails.
 15. The positioning system as in claim 12,wherein the first drive is configured to position the patient supportwith a precision of one micrometer for a range of 0-300 micrometer. 16.The positioning system as in claim 12, wherein the first drive includesa screw drive mechanism operating in a closed loop.
 17. The positioningsystem as in claim 16, wherein the screw drive mechanism includes ascrew arrangement coupled to the patient support and an electric motorcoupled to the screw arrangement.
 18. The positioning system as in claim17, further comprising a programmer for configuring the electric motorto position the patient support based on a velocity profile.
 19. Thepositioning system as in claim 18, wherein the velocity profile includesmapping of velocity of the patient support in the imaging device overvolume of a scanned object.
 20. The positioning system as in claim 12,wherein the second drive is configured to be a prime mover operating ina closed loop.
 21. A method of positioning a patient in an imagingdevice comprising the steps of: (a) aligning a patient table along anX-axis using a coarse positioning subsystem; (b) fine tuning thealignment of the patient table with fine precision along the X-axisusing a fine positioning subsystem; (c) actuating the fine positioningsubsystem to align the patient table using a velocity profile; and (d)adjusting the position of the patient table using the velocity profile.22. The method as in claim 21, wherein the velocity profile includesmapping of velocity of the patient table passing through a scanning beamin the imaging device over volume of a scanned object.